The aim of this research proposal is to elucidate the steps in the infected cell which lead to the assembly of reovirus, which virus consists of ten segments of double stranded RNA's surrounded by two protein coats, an inner coat with four and an outer coat with three proteins. We intend to focus on the events which include the interaction of reovirus protein(s) with reovirus single-stranded RNA's, the identification of the unit which contains the replicase, the mode of assembly of replicating units into particles which synthesize in vitro double-stranded RNA's, and the conversion of these to transcriptase particles and to complete virions. We will use as probe, the ability of a small reovirus-specific component comprised of five subunits to copy in vitro polycytidylate (poly C) as template into the double-stranded polycytidylate: polyguanylate (poly C:poly G). This small component can self-assemble in vitro into icosahedral structures with a diameter close to 75 nm. We will purify the small component and the particles from cells infected with wild type virus and identify what RNA's and proteins they contain and what is their morphology. We will determine if the size of the structures assembled in vitro depends on addition of specific single- or double-stranded RNA's. We will identify the defect(s) in synthesis of double-stranded RNA exhibited at nonpermissive temperature by mutants in groups C, D, and E.